power mosfet integrated high efficiency bcm led driver … · 2018-10-04 · power mosfet...

RT8497

Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.

DS8497-03 July 2017 www.richtek.com 1

Power MOSFET Integrated High Efficiency BCM LED Driver Controller for High Power Factor Applications

General Description

The RT8497 integrates a power MOSFET and a

Boundary mode controller. It is used for step down

converters by well controlling the internal MOSFET and

regulating a constant output current.

The RT8497 features a ZCS detector which keeps

system operating in BCM and obtaining excellent

power efficiency, better EMI performance.

The RT8497 achieves high Power Factor Correction

(PFC) and low Total Harmonic Distortion of Current

(THDi) by a smart internal line voltage compensation

circuit which has minimized system component counts;

saved both PCB size and total system cost.

Especially, the RT8497 can use a cheap simple drum

core inductor in the system instead of an EE core to

obtain high efficiency.

The RT8497 is housed in a SOP-8 package. Thus, the

components in the whole LED driver system can be

made very compact.

Ordering Information RT8497

Package Type

S : SOP-8

Lead Plating System

G : Green (Halogen Free and Pb Free)

MOSFET Built-In

Default : 500V/5.2

A : 500V/2

B : 600V/4.2

C : 600V/7

D : 600/3.2

Note :

Richtek products are :

RoHS compliant and compatible with the current

requirements of IPC/JEDEC J-STD-020.

Suitable for use in SnPb or Pb-free soldering processes

Features Built-In Power MOSFET

Support High Power Factor and Low THDi

Applications

Programmable Constant LED Current with

High-Precision Current Regulation

Extremely Low Quiescent Current Consumption

and 1A Shutdown Current

Compact Floating Buck Topology with Low

Component Counts, Small PCB Size, and Low

System BOM Cost

Unique Programmable AND Pin for ZVS Setting

to Achieve Best Power Efficiency

Support Off-Line Universal Input Voltage Range

Built-in Over Thermal Protection

Built-in Over Voltage Protection

Output LED String Open Protection

Output LED String Short Protection

Output LED String Over Current Protection

Applications E27, PAR, Light Bar, Offline LED Lights

Pin Configuration (TOP VIEW)

SGND

VC

AND

SOURCE

VCC

NC

DRAIN

DRAIN

2

3

4 5

6

7

8

SOP-8

RT8497


www.richtek.com DS8497-03 July 2017 2

Marking Information

RT8497

GSYMDNN

RT8497GS : Product Number

YMDNN : Date Code

RT8497GS

RT8497CGS : Product Number

YMDNN : Date Code

RT8497CGS

RT8497B

GSYMDNN

RT8497BGS : Product Number

YMDNN : Date Code

RT8497BGS

RT8497A

GSYMDNN

RT8497AGS : Product Number

YMDNN : Date Code

RT8497AGS

RT8497C

GSYMDNN

RT8497DGS : Product Number

YMDNN : Date Code

RT8497DGS

RT8497D

GSYMDNN

Functional Pin Description

Pin No. Pin Name Pin Function

1 SGND Ground of the chip.

2 VC Close Loop compensation node.

3 AND Next delay timing function control.

4 SOURCE Internal power MOSFET source connection.

5, 6 DRAIN Internal power MOSFET drain connection.

7 NC No internal connection.

8 VCC Supply voltage input of the chip. For good bypass, a ceramic capacitor near the

VCC pin is required.

RT8497



Functional Block Diagram

DRAIN

Regulator

SGND

AND

State

Machine

VCC

VC

AEA+

-

+-

250mVSOURCE

SOURCE

Operation The RT8497 senses true average output current and

keeps the system driving constant output current. The

VC pin is the compensation node in this close loop

system and dominates the frequency response. To

stabilize the system and achieve better PFC / THDi,

proper selection of a compensation network is needed.

RT8497



Absolute Maximum Ratings (Note 1)

Supply Input Voltage ------------------------------------------------------------------------------------------------ 0.3V to 40V

DRAIN to SOURCE Voltage, VDS, (RT8497B, RT8497C, RT8497D) ---------------------------------- 0.3V to 600V

DRAIN to SOURCE Voltage, VDS, (RT8497, RT8497A) -------------------------------------------------- 0.3V to 500V

DRAIN Current, ID @ TC = 25C -------------------------------------------------------------------------------- 1.4A

DRAIN Current, ID @ TC = 100C ------------------------------------------------------------------------------ 0.9A

Power Dissipation, PD @ TA = 25C

SOP-8 ------------------------------------------------------------------------------------------------------------------- 0.53W

Package Thermal Resistance (Note 2)

SOP-8, JA ------------------------------------------------------------------------------------------------------------- 188C/W

Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------- 260C

Junction Temperature ----------------------------------------------------------------------------------------------- 150C

Storage Temperature Range -------------------------------------------------------------------------------------- 65C to 150C

ESD Susceptibility (Note 3)

HBM (Human Body Model) ---------------------------------------------------------------------------------------- 2kV

Recommended Operating Conditions (Note 4)

Supply Input Voltage ------------------------------------------------------------------------------------------------ 10V to 30V

Ambient Temperature Range-------------------------------------------------------------------------------------- 40C to 85C

Junction Temperature Range ------------------------------------------------------------------------------------- 40C to 125C

Electrical Characteristics (VCC = 24V, TA = 25C, unless otherwise specified)

Parameter Symbol Test Conditions Min Typ Max Unit

VCC UVLO ON VUVLO_ON 17 18 19 V

VCC UVLO OFF VUVLO_OFF 6.4 7.2 8 V

VCC Shut Down Current ISHDN VCC = 15V -- -- 1 A

VCC Quiescent Current IQ Drain stands still -- 0.5 5 mA

VCC Operating Current ICC By CGATE = 1nF, Freq. = 20kHz -- 1 5 mA

VCC OVP Level VOVP 31.5 34 38.5 V

Current Sense Threshold VSENSE 242.5 250 257.5 mV

AND Pin Leakage Current IAND VAND = 5V -- 1 2 A

Static Drain-Source

On-Resistance RDS(ON)

VGS = 12V, ID

= 100mA

RT8497 -- 5.2 --

RT8497A -- 2 --

RT8497B -- 4.2 --

RT8497C -- 7 --

RT8497D -- 3.2 --

RT8497



Parameter Symbol Test Conditions Min Typ Max Unit

Drain-Source Leakage Current IDSS

RT8497, VDS = 500V

-- -- 10 A

RT8497A, VDS = 500V

RT8497B, VDS = 600V

RT8497C, VDS = 600V

RT8497D, VDS = 600V

Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are

stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the

operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may affect

device reliability.

Note 2. JA is measured under natural convection (still air) at TA = 25C with the component mounted on a high

effective-thermal-conductivity four-layer test board on a JEDEC 51-7 thermal measurement standard.

Note 3. Devices are ESD sensitive. Handling precaution recommended.

Note 4. The device is not guaranteed to function outside its operating conditions

RT8497



Typical Application Circuit

3

2

1

8

4

EC1

L1

Bootstrap diode

R2

D1

R1

Optional

CIN

AND VCC

SOURCESGND

VC

C2

DRAIN

5, 6

C1

+

D2

Bridge Rectifier

+

-

RT8497R3

(Optional)

Figure 1. Typical Application of Buck Type

RT8497



Typical Operating Characteristics

Operating Current vs. Supply Voltage

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0 10 20 30 40

Supply Voltage (V)

Op

era

tin

g C

urr

en

t (m

A)

GATE with 1nF

Operating Current vs. Temperature

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

-50 0 50 100 150

Temperature (°C)

Op

era

tin

g C

urr

en

t (m

A)

VCC = 24V, GATE with 1nF

OVP vs. Temperature

30

31

32

33

34

35

36

37

38

39

40

-50 -30 -10 10 30 50 70 90 110 130 150

Temperature (°C)

OV

P (

V)

UVLO vs. Temperature

0

2

4

6

8

10

12

14

16

18

20

-50 0 50 100 150

Temperature (°C)

UV

LO

(V

)

UVLO_ON

UVLO_OFF

Sense Threshold vs. Supply Voltage

0

50

100

150

200

250

300

350

400

450

500

0 10 20 30 40

Supply Voltage (V)

Se

nse

Th

resh

old

(m

V)

Sense Threshold vs. Temperature

0

50

100

150

200

250

300

350

400

450

500

-50 0 50 100 150

Temperature (°C)

Se

nse

Th

resh

old

(m

V)

VCC = 24V

RT8497



Efficiency vs. Input Voltage

75

80

85

90

95

100

85 105 125 145 165 185 205 225 245 265

Input Voltage (V)

Effic

ien

cy (

%)

VIN_AC = 90V to 264V

IOUT = 320mA, LED 16pcs,

L = 470μH

RT8497A

Output Current vs. Input Voltage

270

280

290

300

310

320

330

340

350

360

370

85 105 125 145 165 185 205 225 245 265

Input Voltage (V)

Ou

tpu

t C

urr

en

t (m

A)



L = 470μH

RT8497A

Power Factor vs. Input Voltage

0.70

0.75

0.80

0.85

0.90

0.95

1.00

85 105 125 145 165 185 205 225 245 265

Input Voltage (V)

Po

we

r F

acto

r



L = 470μH

RT8497AVIN_AC = 264V

Input and Output Current

Time (5ms/Div)

VIN

(500V/Div)

VOUT

(50V/Div)

IIN(200mA/Div)

IOUT

(500mA/Div) IOUT = 320mA, LED 16pcs, L = 470μH

Power On

Time (100ms/Div)

VIN

(500V/Div)

VOUT

(20V/Div)

IOUT

(200mA/Div)

VIN_AC = 264V

IOUT = 320mA,

LED 16pcs, L = 470μH

Power Off

Time (100ms/Div)

VIN

(500V/Div

VOUT

(20V/Div)

IOUT

(200mA/Div)

VIN_AC = 264V

IOUT = 320mA,

LED 16pcs, L = 470μH

RT8497



Total Harmonic Distortion

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

3 5 7 9 11 1315 17 19 21 23 25 2729 31 33 35 37 39

Class C

MeasuredVIN_AC = 115V


L = 470μH

Total Harmonic Distortion

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39

Class C

MeasuredVIN_AC = 230V


L = 470μH

RT8497



Application Information The RT8497 is a Boundary mode converter, which can

be used in buck configuration, to provide a constant

output current to the (LED) load. It contains special

circuitry for achieving high power factor and low input

current THD, while minimizing external component

count. The RT8497 integrates a power MOSFET and

housed in a SOP-8 package. Thus, the components in

the whole LED driver system can be made very

compact.

The RT8497 can achieve high accuracy LED output

current via the average current feedback loop control.

The internal sense voltage (250mV typ.) is used to set

the average output current. The average current is set

by the external resistor, RS. The sense voltage is also

used for over current protection (OCP) function. The

typical OCP threshold is about seven times of the

sense voltage threshold.

Under Voltage Lockout (UVLO)

The RT8497 includes a UVLO function with 10.8V

hysteresis. For system start up, the VIN must rise over

18V (typ.) to turn on the internal MOSFET. The internal

MOSFET will turn off if VIN falls below 7.2V (typ.)

Setting Average Output Current

The output current that flows through the LED string is

set by an external resistor, RS, which is connected

between the GND and SOURCE pins. The relationship

between output current, IOUT, and RS is shown below :

OUTS

250I = mA

R

Start-up Resistor

The start-up resistor should be chosen to set the start

up current exceeds certain minimum value. Otherwise,

the RT8497 may latch off and the system will never

start.

The start-up current equals 2 90V / R1 +R2 (for

110VAC regions), and equals 2 180V / R1 +R2

(for 220VAC regions). The typical required minimum

start-up current is 100A. The typical total start up

resistance (R1+ R2) is around 1M Ohm for universal

inputs.

Input Diode Bridge Rectifier Selection

The current rating of the input bridge rectifier is

dependent on the VOUT /VIN conversion ratio and out

LED current. The voltage rating of the input bridge

rectifier, VBR, on the other hand, is only dependent on

the input voltage. Thus, the VBR rating is calculated as

below :

BR AC(MAX)V = 1.2 2 V

where VAC(MAX) is the maximum input voltage (RMS)

and the parameter 1.2 is used for safety margin.

For this example :

BR AC(MAX)V = 1.2 2 V = 1.2 2 264 = 448V

If the input source is universal, VBR will reach 448V. In

this case, a 600V, 0.5A bridge rectifier can be chosen.

Input Capacitor Selection

For High Power Factor application, the input Capacitor

CIN should use a small value capacitance to achieve

line voltage sine-wave.

The voltage rating of the input filter capacitor, VCIN,

should be large enough to handle the input voltage.

VCIN ≥ (1.2× 2 × VAC(MAX) ) = (1.2× 2 × 264) = 448V

Thus, a 0.1F / 500V film capacitor can be chosen in

this case.

Inductor Selection

For high power factor application, the RT8497 operates

the converter in BCM (Boundary-Condition Mode). The

inductance range is defined by peak current of inductor、

maximum and minimum value of switching on time and

off time, for ensuring the inductor operates in BCM. The

peak current of inductor is showed as below :

PEAK

PEAK

2PinI =

V F a

OUT

PEAK

Vwhere a =

V

and

4 3 2F a -0.411a +0.296a -0.312a +0.638a-0.0000846,

a|0~0.7

The inductance range is showed as below :

RT8497



PEAK OUT ONOUT OFF

PEAK PEAK

V V TV TL = =

I I

Where 0.5s TON 35s and 2s TOFF 30s

The frequency at the top of the sine wave can be

calculated :

SWON OFF DELAY

1f =

T + T + T

(Tdelay is determined by the resistor connected to AND

pin , see Turn on delay time)

Turn On Delay Time

After the inductor current has reached zero, a

resonance will occur between the inductor and the

MOSFET drain-source capacitance.

In order to minimize the MOSFET switching losses, the

RT8497 provides the flexibility to adjust the delay time

of next switch-on cycle in order to switch-on at the

maximum point of the resonance, which corresponds to

the minimum drain-source voltage value.

The delay time from zero current point to the maximum

of the switch resonance which can be calculated from :

resonance SWT = L1 C

where CSW is the capacitance at the switch node,

mostly determined by the MOSFET drain-source

capacitance.

The delay time TDELAY from zero current detection

point to next MOSFET switch-on cycle can be adjusted

by the resistor value R3B connected between AND pin

and IC GND

TDELAY(μs)=(-0.4 x R3B2+3500 x R3B+407500) x 10

-6

R3B resister value in k.

Forward Diode Selection

When the power switch turns off, the path for the

current is through the diode connected between the

switch output and ground. This forward biased diode

must have minimum voltage drop and recovery time.

The reverse voltage rating of the diode should be

greater than the maximum input voltage and the

current rating should be greater than the maximum

load current.

The peak voltage stress of diode is :

D AC(MAX)V 1.2 2 V = 1.2 2 264 = 448V

The input source is universal (VIN = 85V to 264V), VD

will reach 448V.

Thermal Protection (OTP)

A thermal protection feature is included to protect the

RT8497 from excessive heat damage. When the

junction temperature exceeds a threshold of 150°C, the

thermal protection OTP will be triggered and the

internal MOSFET will be turned off.

Thermal Considerations

The junction temperature should never exceed the

absolute maximum junction temperature TJ(MAX), listed

under Absolute Maximum Ratings, to avoid permanent

damage to the device. The maximum allowable power

dissipation depends on the thermal resistance of the IC

package, the PCB layout, the rate of surrounding

airflow, and the difference between the junction and

ambient temperatures. The maximum power

dissipation can be calculated using the following

formula :

PD(MAX) = (TJ(MAX) TA) / JA

where TJ(MAX) is the maximum junction temperature,

TA is the ambient temperature, and JA is the

junction-to-ambient thermal resistance.

For continuous operation, the maximum operating

junction temperature indicated under Recommended

Operating Conditions is 125C. The junction-to-

ambient thermal resistance, JA, is highly package

dependent. For a SOP-8 package, the thermal

resistance, JA, is 188C/W on a standard JEDEC 51-7

high effective-thermal-conductivity four-layer test board.

The maximum power dissipation at TA = 25C can be

calculated as below :

PD(MAX) = (125C 25C) / (188C/W) = 0.53W for a

SOP-8 package.

The maximum power dissipation depends on the

operating ambient temperature for the fixed TJ(MAX)

and the thermal resistance, JA. The derating curves in

Figure 2 allows the designer to see the effect of rising

ambient temperature on the maximum power

dissipation.

RT8497



Figure 2. Derating Curve of Maximum Power

Dissipation

Layout Considerations

For best performance of the RT8497, the following

layout guidelines should be strictly followed.

The hold up capacitor, C1, must be placed as close as

possible to the VCC pin.

The compensation capacitor, C2, and delay resistor,

R3B, must be placed as close as possible to the VC

and the AND pin.

The IC SOURCE pin are high frequency switching

nodes. The traces must be as wide and short as

possible.

Keep the main traces with switching current as short

and wide as possible.

Place CIN, L1, RS, COUT, and D1 as close to each

other as possible.

Place the capacitor

C1 as close as possible

to the VCC pin

VMAIN

CIN

Power GND

L1

LED-

LED+RS

C1

COUT

D1

Analog GND

D2

RB

R1

Place the compensation

Components C2 and R3B as

close as possible to the IC

Analog GND

R2

C2

R3B

VCC

Narrow trace from

main circuit to the IC

to avoid the

switching noise

ZD(Option)

Place the Diode D1 and the

resistor RS as close as

possible to the SOURCE pin

RT8497

1 2 3 4

5678

GN

D

VC

AN

D

SO

UR

CE

DR

AIN

DR

AIN

NC

VC

C

Kelvin sense from the sense resistor

directly from the bottom end of the

sense resistor is necessary to avoid

the sense threshold setting error by the

parasitic PCB trace resistance.

Figure 3. PCB Layout Guide

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 25 50 75 100 125

Ambient Temperature (°C)

Ma

xim

um

Po

we

r D

issip

atio

n (

W) 1 Four-Layer PCB

RT8497



Outline Dimension

Symbol Dimensions In Millimeters Dimensions In Inches

Min Max Min Max

A 4.801 5.004 0.189 0.197

B 3.810 3.988 0.150 0.157

C 1.346 1.753 0.053 0.069

D 0.330 0.508 0.013 0.020

F 1.194 1.346 0.047 0.053

H 0.170 0.254 0.007 0.010

I 0.050 0.254 0.002 0.010

J 5.791 6.200 0.228 0.244

M 0.400 1.270 0.016 0.050

8-Lead SOP Plastic Package

Richtek Technology Corporation 14F, No. 8, Tai Yuen 1st Street, Chupei City

Hsinchu, Taiwan, R.O.C.

Tel: (8863)5526789 Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries.

power mosfet integrated high efficiency bcm led driver … · 2018-10-04 · power mosfet...

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